Minimally invasive medical techniques are intended to reduce the amount of extraneous tissue that is damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. Minimally invasive robotic surgical or telesurgical systems have been developed to increase a surgeon's dexterity and to avoid some of the limitations on traditional minimally invasive techniques. In telesurgery, the surgeon uses some form of remote control, e.g., a servomechanism or the like, to manipulate surgical instrument movements, rather than directly holding and moving the instruments by hand. In telesurgery systems, the surgeon can be provided with an image of the surgical site at the surgical workstation. While viewing a two or three dimensional image of the surgical site on a display, the surgeon performs the surgical procedures on the patient by manipulating master control devices, which in turn control motion of the servomechanically operated instruments.
In robotically-assisted telesurgery, the surgeon typically operates a master controller to control the motion of surgical instruments at the surgical site from a location that may be remote from the patient (e.g., across the operating room, in a different room, or a completely different building from the patient). The master controller usually includes one or more hand input devices, such as hand-held wrist gimbals, joysticks, exoskeletal gloves or the like, which are operatively coupled to the surgical instruments that are releasably coupled to a patient side surgical manipulator (“the slave”). The master controller controls the instrument's position, orientation, and articulation at the surgical site. The slave is an electro-mechanical assembly which includes one or more arms, joints, linkages, servo motors, etc. that are connected together to support and control the surgical instruments. In a surgical procedure, the surgical instruments (including an endoscope) may be introduced directly into an open surgical site, through a natural orifice, or through cannulas into a body cavity.
For minimally invasive surgical procedures, the surgical instruments, controlled by the surgical manipulator, may be introduced into the body cavity through a single surgical incision site, multiple closely spaced incision sites on the patient's body, and/or one or more natural orifices in the patient anatomy. For some minimally invasive surgical procedures performed through particularly small entry ports, multiple surgical instruments may be introduced in a closely gathered cluster with nearly parallel instrument shafts. Previous surgical systems and techniques maintained a common center of motion, known as a “remote center,” at an area near the anatomical entry point. Attempts to maintain a center of rotation at the anatomical entry point, through a particularly narrow surgical incision or a particularly narrow natural orifice such as a human throat or cervix, may result in the collision of the proximal ends of the surgical instruments. Improved systems and methods are needed for controlling these surgical instruments while minimizing the occurrence of surgical instrument collisions.